1. Field of the Invention
The present invention relates to a material having a low adhesion property with respect to an organic substance (hereinafter will be referred to as a “low-adhesion material”), and a mold for molding a resin in which at least a mold surface is made of the low-adhesion material.
2. Description of the Background Art
Conventionally, transfer molding or injection molding has been used for molding a resin. These techniques use a mold for molding a resin having a resin flow channel and a cavity. To mold a resin, a fluid resin is injected into the cavity through the resin flow channel. Thereafter, the injected fluid resin is cured, and a molded body having the cured resin is completed.
In the method of molding a resin described above, it is common that a thermosetting resin is used as a material for the fluid resin, and tool steel is used as a material for the mold for molding a resin. When these materials are used, an adhesion property between the cured resin and the surface of the mold for molding a resin (mold surface) should be reduced for easy removal of the molded body from the mold. In other words, releasability between the cured resin and the mold surface should be improved.
For example, an organic material such as polytetrafluoroethylene or silicone rubber having a good non-wetting (dewetting) characteristic with respect to a fluid resin, that is, a bad wetting characteristic with respect to a fluid resin, is considered to be promising as a material improving releasability between a mold for molding a resin and a cured resin. It is to be noted that, in the present specification, having a good non-wetting characteristic means that a contact angle between a solid mold and a liquid fluid resin is large. For example, Japanese Patent Laying-Open No. 07-329099 proposes on page 3 to page 4 a method of coating a mold with such an organic material by spraying or applying the organic material onto a mold surface and then drying the organic material. According to the document, a mold for molding a resin having an excellent releasability is achieved to a certain degree.
In a case where a chip-type electronic component such as an LSI (Large Scale Integration) chip mounted on a lead frame, a printed board, or the like (hereinafter will simply be referred to as a “chip”) is sealed with a resin, a thermosetting resin containing a ceramic filler, for example, an epoxy resin is used as a fluid resin. Since the filler wears a mold surface, a metal-based material with high hardness having wear resistance is formed on the mold surface. For example, a method is used in which a mold surface is coated with a metal-based material with high hardness excellent in wear resistance such as Cr, TiC, or CrN, by means of plating, PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), or the like.
Further, for example Japanese Patent Laying-Open No. 2004-25677 proposes on page 5 to page 6 and in FIGS. 1 and 2 a resin molding method in which a mold for molding a resin made of a porous material having a three-dimensional communicating hole is used and a gas component contained in a fluid resin is emitted during resin molding out of the mold through the communicating hole.
However, according to the aforementioned conventional technique, a cured resin is likely to stick to a mold surface, and thus there are problems as described below.
Firstly, in order to remove the cured resin as a contaminant such as a resin residue, the mold surface should be cleaned periodically. That makes resin molding operation complicated.
Secondly, numerous eject mechanisms are required to remove a molded body from the mold. Thus, the mold becomes larger and has a complicated structure.
Thirdly, when the mold surface is coated with an organic material such as polytetrafluoroethylene or silicone rubber, these organic materials are likely to be worn by a filler contained in the fluid resin. Therefore, it is practically difficult to use these organic materials singly as a material for improving releasability of the mold.
Fourthly, when the mold surface is coated with a metal-based material with high hardness excellent in wear resistance such as Cr, TiC, or CrN, releasability between the metal-based material and the mold surface is insufficient because these metal-based materials do not have a sufficient non-wetting characteristic with respect to a fluid resin.
That is to say, there exists no mold for molding a resin having a low adhesion property between a mold surface and an organic substance constituting a resin and also having the mold surface made of an appropriate material which can be used practically, including a mold for molding a resin having a mold surface made of a porous material.
The present invention has been made in view of the aforementioned problems, and one object of the present invention is to provide a low-adhesion material having a low adhesion property between an organic substance and a surface of the material. Another object of the present invention is to provide a mold for molding a resin having excellent releasability.